Power transmitting device, power receiving device, power supply system, and power supply method

ABSTRACT

Provided are a power transmitting device, a power receiving device, a power supply system, and a power supply method able to supply electric power by emitting electromagnetic waves. A power transmitting device ( 110 ) comprises: a calculating unit ( 122 ) for calculating the maximum value for the emitted output of electromagnetic waves meeting exposure standards on the basis of a response delay time measured by the communication link between the power transmitting device ( 110 ) and a power receiving device ( 150 ); a power transmitting unit ( 128 ) for transmitting power via a power supply link with the power receiving device ( 150 ) at an output not exceeding the maximum value; an anomaly detecting unit ( 126 ) for detecting an anomaly in the power supply link on the basis of communication with the power receiving device ( 150 ) via the communication link; and an output control unit ( 124 ) for controlling the output on the basis of the detection of an anomaly in the power supply link.

FIELD OF THE INVENTION

The present invention relates to a power transmitting device, a powerreceiving device, a power supply system and a power supply method, andmore specifically to a power transmitting device, a power receivingdevice, a power supply system and a power supply method able to transmitelectric power by emitting electromagnetic waves.

BACKGROUND

As the speed of wireless data communication increases, morecommunication performed via land lines is being replaced by wirelesscommunication. However, electric power is supplied by land lines, andwiring needs to be installed to supply power to wireless communicationdevices. In order to advance the wireless revolution to include bothcommunication and the supply of power, technologies for supplyingelectric power wirelessly need to be developed.

Non-contact power transmission techniques have gained attention as a wayto supply electric power wirelessly (see, for example, JapaneseLaid-open Patent Publication No. 2009-261156: Patent Document 1), butthese techniques supply power using non-emitted energy based primarilyon electromagnetic induction. As a result, the power transmissionefficiency declines as the distance between the power transmitter andthe power receiver increases, and the practical range for this techniqueextends from several millimeters to several dozen centimeters. Even inthe case of the electromagnetic field resonance method, the supply ofelectric power is limited to short distances of one meter or less. Thesenon-contact techniques are effective at relatively short-distance powersupply, but they are no substitute for both indoor and outdoor wiring.

Power transmission techniques via microwaves and laser beams in freespace have been researched as another type of non-contact powertransmission method. This research has focused primarily onlong-distance power transmission techniques between the surface of theearth and outer space, but it will take time to develop practical usesdue to problems unique to long-distance power transmission techniques.

Laser power transmission has recently been proposed as a powertransmission method for moving objects such as electric vehicles. Forexample, a laser beam power transmission system has been disclosed inLaid-open Patent Publication No. 2010-166675 (Patent Document 2) whichcomprises an electric vehicle which receives a laser beam, converts thelaser beam to electric power and uses the resulting power to drive thevehicle, and an electric power supply installed outside of the electricvehicle for supplying the laser beam to the electric vehicle whileautomatically adjusting for the relative position between the vehicleand the power supply. The laser power transmission technique in PatentDocument 2 is a relatively short-distance technique in which a laserbeam is emitted from a phase array-type light-emitting device installedin the overhead structure of a bridge or tunnel to a phase array-typelight-receiving device installed in the roof of an electric vehicle.These laser power transmission techniques have not been developed forpractical use because of problems such as alignment difficulties andinefficiency.

The International Electrotechnical Commission has issued “Safety ofLaser Products—Part 1: Equipment classification, requirements, anduser's guide” IEC 60825-1, regarding the safety of laser devices. Theinternational safety standards, and the safety standards of countriesthat comply with the international standards, regulate laser devicesbased on indicators known as maximum permissible exposure (MPE) andaccessible emission limit (AEL). Laser devices are classified accordingto these safety standards, and some laser products may be assigned to aclass lower than that of the actual power of the laser through technicalmeans employed to limit exposure, such as housings and safetyinterlocks. DVD devices, Blu-ray (registered trademark) devices andlaser printers are products that are marketed in accordance with suchsafety standards.

Laser devices with output in the 1 W range are also used in laserdisplays and laser light shows in concert halls. Laser devices whichemit a scanning laser beam are classified according to the emission ofthe scanning laser beam. As a result of scanning failures, such aschanges in scanning speed or scanning amplitude, safety precautions havebeen taken so that exposure exceeding the accessible emission limit(AEL) for a given class does not occur.

A power transmission technique using the emission of electromagneticwaves such as laser beams is desired in order to create truly wirelesscommunication devices able to communicate data at high speeds andreceive power wirelessly. However, the emission output has to beincreased in order to supply power adequately. Therefore, thedevelopment of a technique is desired which can transmit power via theemission of electromagnetic waves at even higher outputs while alsomeeting exposure standards.

An emergency stop function for the supply of power via light has beendisclosed in Laid-open Patent Publication No. 11-230856 (Patent Document3). In Patent Document 3, a configuration is disclosed in which thepresence of optical feedback anomalies is detected via a separateoptical fiber housed in the same cable as the optic fiber transmittingthe optical power. However, the technique in Patent Document 3 relatesto the supply of optical power via wiring, and does not contribute toadvancing the wireless revolution to include the supply of electricpower.

CITED DOCUMENTS Patent Documents

Patent Document 1: Laid-open Patent Publication No. 2009-261156

Patent Document 2: Laid-open Patent Publication No. 2010-166675

Patent Document 3: Laid-open Patent Publication No. 11-230856

SUMMARY Problem Solved by the Invention

The present invention was devised in view of the insufficiencies of theprior art, and it is an object of the present invention to provide apower transmitting device, an power receiving device, a power supplysystem, and a power supply method able to transmit power via theemission of electromagnetic waves while also meeting predeterminedstandards for exposure premised on the occurrence of anomalies. It isanother object of the present invention to provide a power transmittingdevice, a power receiving device, a power supply system, and a powersupply method able to further improve safety.

Means of Solving the Problem

In order to solve these problems, the present invention provides a powertransmitting device able to transmit power to a power receiving deviceby emitting electromagnetic waves. This power transmitting device hasthe following characteristics. The power transmitting device calculatesthe maximum value for the emitted output of electromagnetic wavesmeeting exposure standards on the basis of a response delay timemeasured by the communication link between the power transmitting deviceand the power receiving device. The power transmitting device alsotransmits power via a power supply link with the power receiving deviceat an output not exceeding the maximum value. In addition, the powertransmitting device detects anomalies in the power supply link on thebasis of communication with the power receiving device via thecommunication link, and limits the emission output of electromagneticwaves on the basis of the detection of anomalies in the power supplylink.

The present invention also provides a power receiving device able toreceive electric power supplied from a power transmitting device byemitting electromagnetic waves. This power receiving device has thefollowing characteristics. The power receiving device is able tocommunicate so as to evaluate the response delay time in communicationvia the communication link between the power receiving device and thepower transmitting device. The power receiving device also receiveselectric power supplied via a power supply link with the powertransmitting device at an emission output of electromagnetic waves notexceeding the maximum value meeting exposure standards, in accordancewith the response delay time. In addition, the power receiving deviceacquires the amount of power received by the power receiving device inorder to limit the output from the power transmitting device in responseto an anomaly occurring in the power supply link.

The present invention further provides a power supply system including apower transmitting device able to transmit power by emittingelectromagnetic waves, and a power receiving device able to receivepower supplied by the power transmitting device.

In addition, the present invention provides a power supply methodexecuted between a power transmitting device able to transmit power byemitting electromagnetic waves, and a power receiving device able toreceive power supplied by the power transmitting device. This powersupply method includes the steps of evaluating the response delay timefor communication via the communication link between the powertransmitting device and the power receiving device, calculating themaximum value for the emitted output of electromagnetic waves meetingexposure standards on the basis of the response delay time, andtransmitting power using the power transmitting unit via a power supplylink with the power receiving device, at an output not exceeding themaximum value. The power supply method also includes the steps ofdetecting anomalies in the power supply link on the basis ofcommunication with the power receiving device via the communicationlink, and causing the power supply device to limit the output of thepower supply link on the basis of the detection of an anomaly in thepower supply link.

Effect of the Invention

The configuration described above is able to transmit power via theemission of electromagnetic waves while also meeting predeterminedstandards for exposure premised on the occurrence of anomalies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a laser power supply systemaccording to an embodiment of the present invention.

FIG. 2 is a diagram showing the function blocks and data flow for alaser power transmitting device and laser power receiving device in alaser power supply system according to an embodiment of the presentinvention.

FIG. 3 is a diagram used to explain the laser output control method.

FIG. 4 is a flowchart showing the controls executed by the laser powertransmitting device according to an embodiment of the present invention.

FIG. 5 is a diagram schematically illustrating the relationship to laseroutput of the exchange of information between the laser powertransmitting device and the laser power receiving device and the timingsthereof in an embodiment of the present invention.

FIG. 6 is a diagram showing the function blocks and data flow for alaser power transmitting device and laser power receiving device in alaser power supply system according to another embodiment of the presentinvention.

FIG. 7 is a diagram schematically illustrating the relationship to laseroutput of the exchange of information between the laser powertransmitting device and the laser power receiving device and the timingsthereof in another embodiment of the present invention.

FIG. 8 is a function block diagram related to the alignment of thewireless communication link and the wireless power supply link in anembodiment of the present invention.

FIG. 9 is a flowchart showing the alignment controls performed by thelaser power transmitting device in an embodiment of the presentinvention.

FIG. 10 is a graph in which total power feeding (W) that meets Class 1safety standards has been plotted with respect to emission duration (s).

FIG. 11 is a diagram used to explain laser emission alignment in theprior art.

DETAILED DESCRIPTION

The following is an explanation of preferred embodiments of the presentinvention, but the present invention is not limited to the embodimentsexplained below. In the embodiments explained below, an example of apower transmitting device, a power receiving device and a power supplysystem are explained using laser power transmitting device 110, laserpower receiving device 150, and laser power supply system 100.

FIG. 1 is a schematic diagram showing a laser power supply system 100according to an embodiment of the present invention. The laser powersupply system 100 in the present embodiment includes a laser powertransmitting device 110, and a laser power receiving device 150installed at a location some distance from the laser power transmittingdevice 110.

The laser power transmitting device 110 includes a laser element 114,and receives a supply of power from a power source 102, and emits alaser beam from the laser element 114 to transmit electric powerwirelessly to the laser power receiving device 150. The laser powerreceiving device 150 includes a photoelectric conversion element 154,and receives the laser beam emitted by the laser power transmittingdevice 110 via the photoelectric conversion element 154 to receiveelectric power wirelessly.

Here, the link established between the laser power transmitting device110 and the laser power receiving device 150 to supply electric power isreferred to as the wireless power supply link. The wireless power supplylink is established between the laser power transmitting device 110 andthe laser power receiving device 150 by aligning the laser emissiondirection so that the laser beam emitted by the laser element 114 isproperly incident on the photoelectric conversion element 154. In thepresent embodiment, the wireless power supply link is not defined by awaveguide, but by the optical path of a laser beam propagated throughthe air.

The laser emission described above can be monochromatic electromagneticwaves such as infrared, visible or ultraviolet light, or a mixture ofthese electromagnetic waves. In the explanation of the presentembodiment, power is supplied via laser emission. However, theelectromagnetic waves emitted to supply power are not limited to laserbeams. In another embodiment, power may be supplied via the emission ofelectromagnetic waves in another waveband, such as microwaves.

The laser power receiving device 150 supplies the received electricpower to a load 190 connected externally or incorporated internally.There are no particular limitations on the load 190. It can be anydevice or component that consumes or stores electric power, such as aprojector, monitoring camera, or secondary battery.

The laser power transmitting device 110 and laser power receiving device150 in the present invention are provided with antennas 112 and 152,respectively, which are configured to establish wireless datacommunication. Here, the link established between the laser powertransmitting device 110 and the laser power receiving device 150 for thecommunication of data is referred to as the wireless communication link.The wireless communication link is different from the wireless powersupply link mentioned above. The wireless communication link preferablyhas high directionality. However, the wireless power supply linktypically has higher directionality than the wireless communicationlink. In a preferred embodiment, the wireless communication link useselectromagnetic waves (millimeter waves) in a frequency band of severaldozen GHz (typically 60 GHz) to realize data communication rates inexcess of several Gbps.

There are no particular restrictions on antennas 112 and 152. However,in a preferred embodiment, an antenna with controllable directionalityis employed, such as an active array antenna in which a plurality ofantennas is arranged. In the wireless communication link, the laserpower transmitting device 110 and the laser power receiving device 150are able to exchange data as either transmitter or receiver.

The laser power transmitting device 110 shown in FIG. 1 controls theemitted laser output and wirelessly supplies electric power to the laserpower receiving device 150 while exchanging information with the laserpower receiving device 150 via data communication in the wirelesscommunication link. The distance between the laser power transmittingdevice 110 and the laser power receiving device 150 depends on thedirectionality of the laser beam and wireless electromagnetic waves, andthe environment in which the devices are being used. This distance canbe any distance within a range in which the laser beam can effectivelytransmit an adequate amount of power and in which wireless datacommunication can be maintained at an adequate rate.

The laser device in the laser power transmitting device 110 is subjectto international standards regarding the safety of laser devices(“Safety of Laser Products—Part 1: Equipment classification,requirements, and user's guide” IEC 60825-1) and domestic safetystandards that comply with these international standards (JIS C 6802).

In the JIS C 6802 standards, “Class 1 laser products” are defined as“all laser products which, during operation, do not expose the humanbody to laser emissions in excess of the Class 1 accessible emissionlimit (AEL) relative to wavelength and emission duration”). Here,“emission duration” is defined as “the duration of pulses, pulse trainsor continuous emission of a laser to which the human body is exposed asa result of operating, maintaining or servicing a laser device.” In thecase of a single pulse, the emission duration is the span of timebetween the rising edge half-point and the falling edge half-point ofthe pulse. In the case of a continuous pulse train (or a group ofsub-pulses in the main pulse train), the emission duration is the spanof time between the rising edge half-point of the initial pulse and thefalling edge half-point of the final pulse.

The “accessible emission limit (AEL)” is defined as the “maximumexposure permitted for each class,” and “accessible emission” is definedas “the emission level defined at a given position using a specifiedaperture stop [when the AEL is provided in watts (W) or joules (J)] orusing a limiting aperture [when the AEL is provided in watts per squaremeter (W·m⁻²) or joules per square meter (J·m⁻²)]. The maximumpermissible exposure (MPE) is defined as “the level of laser exposure ina normal environment which does not cause harm to an exposed humanbody.” The “MPE level” is “the maximum level at which exposure causes noimmediate or long-term damage to eyes and skin.” The accessible emissionlimit (AEL) is generally derived from the maximum permissible exposure(MPE).

In the laser power supply system 100 shown in FIG. 1, a laser beampropagates in the air from the laser power transmitting device 110 tothe laser power receiving device 150. When, at this time, an obstaclecomes between the laser power transmitting device 110 and the laserpower receiving device 150 and blocks the optical path, the laser beammay be emitted outside of the optical path due, for example, toreflection on the surface of the obstacle. The obstacle itself may alsobe exposed to the laser beam. Therefore, immediately after theoccurrence of an anomaly, such as an obstacle blocking the optical path,controls are required to reduce the emission level that may occur duringthe reaction time below a predetermined reference level until the laseroutput has been sufficiently restricted.

Therefore, in the laser power supply system 100 in the presentembodiment, any anomaly occurring in the wireless power supply link andwireless communication link is detected on the basis of datacommunication via the wireless communication link while power is beingtransmitted via the power supply link within a predetermined outputrange, and the laser output is restricted in response to the occurrenceof an anomaly. The following is a detailed explanation of the powersupply method executed by the power transmitting device 110 and powerreceiving device 150 in the present embodiment with reference to FIG. 2through FIG. 10.

FIG. 2 is a diagram showing the function blocks and data flow for alaser power transmitting device 110 and laser power receiving device 150in a laser power supply system 100 according to an embodiment of thepresent invention. The laser power transmitting device 110 shown in FIG.2 includes a wireless data communication unit 120, a maximum outputcalculating unit 122, a laser output control unit 124, an anomalydetecting unit 126, and a laser emitter for power transmission 128. Thelaser power receiving device 150 shown in FIG. 2 includes a wirelessdata communication unit 160 and a photoelectric converter for powerreception 162.

Wireless data communication units 120 and 160 in the laser powertransmitting device 110 and the laser power receiving device 150,respectively, are wireless communication interfaces for bidirectionalwireless data communication. During reception, wireless datacommunication units 120 and 160 receive carrier waves propagated throughthe air via antenna 112 and 152, respectively, and restore the receiveddata on the basis of a predetermined modulation scheme. Duringtransmission, the wireless data communication unit 120 modulates thetransmitted data on the basis of a predetermined modulation scheme, andemits the signals through the air as carrier waves. There are noparticular restrictions on the modulation scheme. Examples of modulationschemes include M-ary Phase Shift Keying (MPSK) and M-ary QuadratureAmplitude Modulation (MQAM).

The laser emitter for power transmission 128 in the laser powertransmitting device 110 typically includes a GaAs, InGaAs or InGaAsPsemiconductor laser element. However, in another embodiment, the laserelement 114 may use a gas laser or solid-state laser. The mode ofoperation for the laser element may be a continuous wave (CW) mode ofoperation or a pulsed wave mode of operation. There are no particularrestrictions on the laser emitting wavelength of the laser element.

The photoelectric converter for power reception 162 in the laser powerreceiving device 150 includes a photoelectric conversion element thatphotoelectrically converts the received laser beam to generateelectromotive force. The photoelectric conversion element may be aphotodiode or solar cell having high conversion efficiency with respectto the wavelength of the laser emitted by the laser emitter for powertransmission 128.

The maximum output calculating unit 122 evaluates the response delaytime observed in the wireless communication link between the powertransmitting device 110 and the power receiving device 150, andcalculates the maximum value (maximum permissible value) for the laseremission output that meets allowable exposure standards on the basis ofthe evaluated response delay time. Here, the maximum permissible valuefor the laser emission output is calculated so as not to exceed apredetermined standard exposure level when the laser is emitted at theoutput of the maximum permissible value for the duration of the reactiontime required for the laser output to be limited to a sufficiently lowlevel after the occurrence of an anomaly.

In the present embodiment, any anomaly that has occurred in the wirelesspower supply link is detected on the basis of data communication via thewireless communication link. Therefore, the reaction time depends on theresponse delay time (latency) of the data communication between thepower transmitting device 110 and the power receiving device 150 via thewireless communication link. More specifically, the reaction timeincludes the response delay time that passes during data communicationfor detecting anomalies, the time required to detect an anomaly on thebasis of transmitted data, the time required for the laser output to bereduced to below a predetermined level after anomaly detection, and apredetermined time margin. Typically, the response delay time forwireless communication is predominant.

The maximum permissible value calculated under these conditions is themaximum allowable output value which guarantees that the emission levelthat may be emitted during the response time is below a predeterminedreference level in accordance with the response delay time. Therefore,if the laser is emitted at an output that does not exceed this maximumpermissible value, from the time an anomaly occurs until output controlis performed, the laser beam is kept from exposing the obstacle at alevel exceeding the exposure standard or being emitted outside theoptical path, even when an anomaly has occurred in the wireless powersupply link. The maximum permissible value can be increased as theresponse time becomes shorter to enable the supply of power at a higheroutput.

For the response delay time, the time required to transmit data of aknown length (for example, measurement data) can be measured, the datatransfer rate can be calculated based on the required time, and theresponse delay time can be evaluated based on the data transfer rate.The response delay time thusly evaluated depends on the communicationmethod used in anomaly detection, but round-trip latency or one-waylatency can also be used. In the present embodiment, the maximumpermissible value may be calculated from the response delay time or datatransfer rate using a predetermined equation, or may be obtained byreferencing a table associating response delay times or data transferrates with maximum permissible values.

When the relative positional relationship of the power transmittingdevice 110 and the power receiving device 150 is fixed, the evaluationof the response delay time and the calculation of the maximumpermissible value may typically be performed one time beforeestablishing a wireless power supply link and supplying power. However,when the relative positional relationship is variable, the evaluation ofthe response delay time and the calculation of the maximum permissiblevalue based on the evaluated response delay time may be repeated at asuitable frequency. In this situation, the data transmission rate can bemeasured via data communication for anomaly detection, and the latestcalculated maximum permissible value used.

The laser output control unit 124 is used to control the operation ofthe laser emitter for power transmission 128, and controls the laseroutput based on the maximum permissible value for the laser outputcalculated by the maximum output calculating unit 122 so as not toexceed the maximum permissible value. The laser output control unit 124can increase the laser output in stages from zero to the maximumpermissible value while confirming the amount of power received on thepower receiving end on the basis of data communication via the wirelesscommunication link.

The laser emitter for power transmission 128 is configured as a powertransmitting unit which, under the control of the laser output controlunit 124, emits the laser and transmits power to the laser powerreceiving device 150 at an output that does not exceed the maximumpermissible value. There are no particular restrictions on the laseroutput control method.

FIG. 3 is a diagram used to explain the laser output control method. Asshown in the left-hand column of the table shown in FIG. 3, duringcontinuous laser emission, the power of the laser emission can beincreased or decreased using the photon density. As shown in the centraland right-hand columns of the table in FIG. 3, during laser pulseemission, the power of the laser emission can be increased or decreasedusing the pulse width (duty ratio) in a predetermined pulse phase or canbe increased or decreased using the pulse phase or pulse frequency(number of pulses per unit of time).

The anomaly detecting unit 126 can monitor the state of the wirelesspower supply link and detect the occurrence of an anomaly on the basisof data communication with the laser power receiving device 150 via thewireless communication link. An anomaly can be detected by taking intoaccount the conversion efficiency of both device 110 and 150, andcomparing the amount of power (electric power) transmitted by the laserpower transmitting device 110 and the amount of power (electric power)received by the laser power receiving device 150.

When the difference or ratio of emitted power received by the laserpower receiving device 150 (received power/photoelectric conversionefficiency) relative to the emitted power transmitted by the laser powertransmitting device 110 (inputted power×photoelectric conversionefficiency, or known emitted power at a set output value) is outside ofa predetermined criterion, a loss of power for reasons which cannot beignored is suggested, and the occurrence of an anomaly in the wirelesspower supply link can be determined. This loss typically occurs becauseof the optical path being blocked by an obstacle, contamination of theoptical path by smoke or dust which causes scattering and diffusereflection, misalignment of the laser, or deterioration or failure ofthe photoelectric conversion element. When such an anomaly occurs,limiting the laser output is preferred from a management standpoint.

In the embodiment shown in FIG. 2, the amount of received power isacquired by the photoelectric converter for power reception 162 servingas the amount of received power acquiring unit in the laser powerreceiving device 150, and the acquired amount of power received isreported to the laser power transmitting device 110 by the wireless datacommunication unit 160. The anomaly detecting unit 126 in the laserpower transmitting device 110 acquires the amount of power transmittedfrom the laser emitter for power transmission 128, and compares theamount of power received which was reported by the laser power receivingdevice 150 to the acquired amount of power transmitted while taking intoaccount conversion efficiency. When the results of the comparisonindicate the occurrence of loss equal to or greater than a predeterminedthreshold value, it is determined that an anomaly has occurred in thewireless power supply link.

The anomaly detecting unit 126 can also detect anomalies in the wirelesscommunication link in addition to detecting anomalies in the wirelesspower supply link by comparing the amount of power received to theamount of power transmitted. Anomalies that can occur in the wirelesscommunication link include an interruption in the wireless communicationlink itself, a rapid decline in the signal-to-noise ratio (SNR), andrapid changes in the beam direction of an adaptively controlled antenna.

In the present embodiment, an anomaly is detected in the wireless powersupply link using the wireless communication link. Therefore, any ofthese anomalies can obstruct anomaly detection in the wireless powersupply link. When the anomaly detecting unit 126 in the presentembodiment has detected the occurrence of an anomaly in at least one ofthe wireless communication link and the wireless power supply link, alaser output limiting command, more specifically, a laser output stopcommand, is quickly issued to the laser output control unit 124.

In response to a command due to detection of an anomaly in the wirelesspower supply line or wireless communication link, the laser outputcontrol unit 124 serves as an output control unit to reduce the outputof the laser emitted from the laser emitter for power transmission 128below a reference level. More specifically, the laser output controlunit 124 responds to a laser output stop command by immediately stoppingthe flow of operating current to the laser element in the laser emitterfor power transmission 128, thereby stopping emission of the laser.

The following is a detailed explanation of the operations performed whenpower is supplied in the laser power supply system 100 described abovewith reference to FIG. 4 and FIG. 5. FIG. 4 is a flowchart showing thecontrols executed by the laser power transmitting device 110 accordingto an embodiment of the present invention. FIG. 5 is a diagramschematically illustrating the relationship to laser output of theexchange of information between the laser power transmitting device 110and the laser power receiving device 150 and the timings thereof in anembodiment of the present invention.

The controls shown in FIG. 4 start from Step S100, for example, inresponse to an operator starting the laser power transmitting device110. In Step S101, the laser power transmitting device 110 exchangesalignment and characteristic information (type of power-transmittinglaser, conversion efficiency, etc.) of the wireless communication linkand wireless power supply link with the laser power receiving device150. The alignment process is explained in greater detail below.

In Step S102, the laser power transmitting device 110 performs datacommunication using the wireless data communication unit 120, andcalculates the data transmission rate of the wireless communication linkusing the maximum output calculating unit 122. In Step S103, the laserpower transmitting device 110 evaluates the response delay time observedin communication via the wireless communication link on the basis of thedata transmission rate measured by the maximum power calculating unit122. In Step S104, the laser power transmitting device 110 uses themaximum output calculating unit 122 to calculate the maximum permissiblevalue for laser output in response to the evaluated response delay time.

In Step S105, the laser power transmitting device 110 uses the wirelessdata communication unit 120 to output a wireless communication linkconfirmation to the laser power receiving device 150 (indicated by theblack squares in FIG. 5). After receiving the link confirmation, thelaser power receiving device 150 outputs a wireless communication linkresponse to the laser power transmission device 110 (indicated by thegray squares in FIG. 5). In Step S106, the laser power transmittingdevice 110 determines whether or not there has been a link response tothe link confirmation. When it has been determined in Step S106 thatthere has been no link response (NO), it is treated as an anomaly orerror in the wireless communication link, and the control process isended in Step S113 without beginning laser output.

When it has been determined in Step S106 that there has been a linkresponse (YES), the control process advances to Step S107. In Step S107,the laser power transmitting device 110 sets the calculated maximumpermissible value, and begins laser emission from the laser emitter forpower transmission 128 under the control of the laser control unit 124from the initial level.

In Step S108, the laser power transmitting device 110 receives theamount of power received (indicated by the numbered squares in FIG. 5)which is transmitted from the laser power receiving device 150 using thewireless data communication unit 120 following the link response. InStep S109, the laser power transmitting device 110 acquires the amountof transmitted power from the laser emitter of power transmission 128.In Step S110, the laser power transmitting device 110 uses the anomalydetecting unit 126 to determine whether or not an anomaly has occurredin one of at least the wireless power supply link and wirelesscommunication link. When no anomaly has been determined in Step S110(YES), the control process advances to Step S111.

In Step S111, the laser power transmitting device 110 uses the laseroutput control unit 124 to increase the laser output in stages within arange that does not exceed the maximum permissible value, and loops thecontrol process to Step S108. FIG. 5 shows the amount of power receivingbeing continuously transmitted from the laser power receiving device 150to the laser power transmitting device 110, and the laser output beingincreased in stages based on the results of a comparison between theamount of power received and the amount of power transmitted.

When the presence of an anomaly has been determined in Step S110 (NO),the control process branches to Step S112. When no notification of theamount of power received has been received (an anomaly on the wirelesscommunication link) or the loss from the comparison of the amount ofpower received to the amount of power transmitted exceeds apredetermined reference level (an anomaly in the wireless power supplylink), it is determined that there has been an anomaly. Here, thecontrol process may branch to Step S112 even when there is an explicitstop command from the operator.

In Step S112, the laser power transmitting device 110 uses the laseroutput control unit 124 to block the supply of drive current to thelaser element to stop oscillation of the laser, and ends the controlprocess in Step S113.

FIG. 5(A) shows the processing flow from the detection of an anomalythat has occurred due to an interruption in the wireless power supplylink to the stopping of the laser. As shown in FIG. 5(A), when thewireless power supply link has been interrupted, a loss occurs in theemitted power received by the laser power receiving device 150, and thelaser power transmitting device 110 is notified of the lower thanexpected amount of power received. In this situation, the laser powertransmitting device 110 can compare the reported amount of powerreceived to the amount of power transmitted by the device itself, detectan anomaly in the wireless power supply link, and immediately stop laseremission.

FIG. 5(B) shows the processing flow from the detection of an anomalythat has occurred due to a malfunction in the wireless communicationlink to the stopping of the laser. As shown in FIG. 5(B), the properamount of power is received by the laser power receiving device 150 evenwhen the wireless communication link is interrupted, but the amount ofpower received is not transmitted to the laser power transmitting device110. In this situation, the laser power transmitting device 110determines that it cannot receive the amount of power received in apredetermined amount of time, can determine that there has been ananomaly in the wireless communication link, and can immediately stoplaser output.

In the embodiment shown in FIG. 2 through FIG. 5, the amount of powerreceived is continuously transmitted from the laser power receivingdevice 150 to the laser power transmitting device 110 via the wirelesscommunication link. At this time, there is no need for communicationfrom the transmitter to the receiver in order for the transmitter tolearn the amount of power received. Therefore, in the embodimentdescribed above, the response delay time evaluated when the maximumpermissible value is calculated may utilize one-way latency from thelaser power receiving device 150 to the laser power transmitting device110. In the embodiment shown in FIG. 2 through FIG. 5, this ispreferable from the standpoint of reducing the reaction time sincecommunication is performed over a one-way link.

After link confirmation, the laser power transmitting device 110 nolonger has to transmit data in order to detect an anomaly. Therefore,after link confirmation, the link in the transmission direction can bestopped by the wireless data communication unit 120 to save power. In anembodiment that omits the initial link confirmation, a link in thetransmission direction can be eliminated from the wireless datacommunication unit 120 altogether.

In the embodiment described above, the laser power transmitting device110 received the amount of power received via the wireless communicationlink to detect an anomaly. However, the anomaly detection method is notlimited to the example described above. The following is an explanationof another embodiment in which anomaly detection is performed by thelaser power receiving device 150 with reference to FIG. 6 and FIG. 7.

FIG. 6 is a diagram showing the function blocks and data flow for alaser power transmitting device 110 and laser power receiving device 150in a laser power supply system 100 according to another embodiment ofthe present invention. The configurational element identical to those inthe embodiment shown in FIG. 2 are denoted by the same numbers. Thefollowing explanation will focus on the points of difference.

The laser power transmitting device 110 shown in FIG. 6 includes awireless data communication unit 120, a maximum output calculating unit122, a laser output control unit 124, an anomaly detecting unit 126, anda laser emitter for power transmission 128. In addition to a wirelessdata communication unit 160 and a photoelectric converter for powerreception 162, the laser power receiving device 150 shown in FIG. 6includes an anomaly detecting unit 164. Wireless communication units 120and 160, the maximum output calculating unit 122, the laser outputcontrol unit 124, the laser emitter for power transmission 128, and thephotoelectric converter for power reception 162 have the same roles asthe same configurational elements in the embodiment explained withreference to FIG. 2.

As in the embodiment described above, the anomaly detecting unit 126 inthe laser power transmitting device 110 monitors the state of thewireless power supply link and detects the occurrence of anomalies basedon data communication with the laser power receiving device 150 via thewireless communication link. However, in the embodiment shown in FIG. 6,anomalies in the wireless power supply link are detected using a methoddifferent from that of the embodiment shown in FIG. 2.

First, the laser power transmitting device 110 acquires the amount ofpower transmitted from the laser emitter for power transmission 128, andsends the acquired amount of power transmitted to the laser powerreceiving device 150 via the wireless data communication unit 120. Theanomaly detecting unit 164 in the laser power receiving device 150compares the amount of power received which is acquired from thephotoelectric converter for power reception 162 to the amount of powertransmitted which is reported by the laser power transmitting device 110in order to determine from the results whether the loss is equal to orgreater than a predetermined threshold value.

When the loss is equal to or greater than a predetermined thresholdvalue, it is determined that an anomaly has occurred in the wirelesspower supply link. In this situation, the laser power receiving device150 reports the occurrence of an anomaly to the laser power transmittingdevice 110 via the wireless data communication unit 160. The anomalydetecting unit 126 in the laser power transmitting device 110 receivesthe report of an anomaly from the laser power receiving device 150, anddetermines that an anomaly has occurred in the wireless power supplylink.

FIG. 7 is a diagram schematically illustrating the relationship to laseroutput of the exchange of information between the laser powertransmitting device 110 and the laser power receiving device 150 and thetimings thereof in another embodiment of the present invention. First,the laser power transmitting device 110 uses the data communication unit120 to output a wireless communication link confirmation to the laserpower receiving device 150 (indicated by the black squares in FIG. 7).When the link confirmation has been received, the laser power receivingdevice 150 outputs a wireless communication link response to the laserpower transmitting device 110 (indicated by the gray squares in FIG. 7).When the link response has been received, the laser power transmittingdevice 110 starts sending the amount of power transmitted to the laserpower receiving device 150 (indicated by the numbered squares in FIG.7).

The laser power receiving device 150 receives notification of the amountof power transmitted from the laser power transmitting device 110,compares the received amount of power transmitted to the actual amountof power received to determine whether the power has been transmittedadequately, and returns the results of the determination to the laserpower transmitting device 110. When determination results indicatingthat the power has been transmitted adequately are received, the laserpower transmitting device 110 uses the laser output control unit 124 toincrease the laser output in stages within a range that does not exceedthe maximum permissible value.

FIG. 7 also shows the processing flow from the detection of an anomalythat has occurred due to an interruption in the wireless power supplylink to the stopping of the laser. As shown in FIG. 7, when the wirelesspower supply link has been interrupted, a loss occurs in the emittedpower received by the laser power receiving device 150, and the amountof power received is less than expected based on the reported amount ofpower transmitted. When the laser power receiving device 150 hasdetected the occurrence of an anomaly, the occurrence of an anomaly isreported to the laser power transmitting device 110. The laser powertransmitting device 110 detects an anomaly based on this report, and canimmediately stop the laser emission.

In the other embodiment described above, the amount of power transmittedis continuously sent via the wireless communication link from the laserpower transmitting device 110 to the laser power receiving device 150.The determination results are reported by the laser power receivingdevice 150 to the laser power transmitting device 110 via the wirelesscommunication link. At this time, two-way communication occurs in orderfor the transmitter to detect anomalies. Therefore, the response delaytime evaluated when calculating the maximum permissible value mayutilize round-trip latency.

The following is a detailed explanation of alignment of the wirelesscommunication link and wireless power supply link between the powertransmitting device 110 and the power receiving device 150 withreference to FIG. 8 and FIG. 9. FIG. 8 is a function block diagramrelated to the alignment of the wireless communication link and thewireless power supply link in an embodiment of the present invention.

As shown in FIG. 8, the laser emitter for power transmission 128includes an initial alignment unit 130 and a subsequent alignment unit132. The initial alignment unit 130 performs rough alignment of thewireless power supply link via the establishment of a wirelesscommunication link between wireless data communication units 120 and160. The subsequent alignment unit 132 then performs fine adjustments onthe alignment of the wireless power supply link based on the results ofthe rough adjustments performed by the initial alignment unit 130 andfeedback from the laser power receiving device 150 via the wirelesscommunication link.

In a preferred embodiment, wireless data communication units 120 and 160can be equipped with a beam-forming antenna such as the active arrayantenna mentioned above. A beam-forming antenna includes a plurality ofantenna elements. Different-phase signals are inputted to each antennaelement, and the antenna is able to control the directionality of thebeam by synthesizing the signals in space. When a beam-forming antennais used, the orientation of the beam can be changed electronically usingphase control. There are no particular restrictions on how beam formingis implemented. It may be implemented using the radio frequency (RF)front end, or digital signal processing.

Because the directionality of the wireless communication link isoptimized by beam forming via the establishment of a wirelesscommunication link, alignment information (phase information) isobtained which defines directionality. The initial alignment unit 130acquires this alignment information from the wireless data communicationunit 120, and determines the initial value for the direction of laseremission based on the acquired alignment information. In this way, thesubsequent alignment can be started from a state in which the directionof laser emission has been roughly adjusted.

The laser power transmitting device 110 emits the laser from the laseremitter for power transmission 128 after initial adjustment. The laserpower receiving device 150 receives the laser emission using thephotoelectric converter 162, and sends, as feedback, the amount of powerreceived to the laser power transmitting device 110 using the wirelessdata communication unit 160. The subsequent alignment unit 132 optimizesthe direction of laser emission in a direction that will improve theamount of power received based on the feedback on the amount of powerreceived.

Typically, the direction of laser emission is determined by mechanicallycontrolling the orientation of a reflective mirror installed outside ofthe laser element, and deflecting the beam emitted by the laser elementusing the reflective mirror. Instead of external optics, a semiconductorlayer may be used in which the beam exit direction can be controlled bya laser resonator using a photonic crystal.

FIG. 9 is a flowchart showing the alignment controls performed by thelaser power transmitting device 110 in an embodiment of the presentinvention. The processing shown in FIG. 9 starts from Step S200 inresponse to being called in Step S101 shown in FIG. 4. In Step S201, thelaser power transmitting device 110 establishes a wireless communicationlink with the laser power receiving device 150 using beam forming. Inthe embodiment explained here, the wireless communication link isestablished prior to the supply of power. The power needed by the laserpower receiving device 150 prior to the wireless supply of power may bedrawn from another suitable means such as a secondary battery chargedpreviously by the supply of wireless power or a primary batteryinstalled in the laser power receiving device 150.

In Step S202, the laser power transmitting device 110 uses the initialalignment unit 130 to roughly align the wireless power supply link basedon alignment information obtained as a result of beam forming. In StepS203, the laser power transmitting device 110 starts the emission of thelaser from the laser emitter for power transmission 128.

In Step S204, the laser power transmitting device 110 uses the wirelessdata communication unit 120 to receive the amount of power received fromthe laser power receiving device 150 via the wireless communicationlink. In Step S205, the subsequent alignment unit 132 is used todetermine whether predetermined convergence conditions have been met.Here, the convergence conditions are used to determine the emissiondirection for the maximum amount of power received and to terminate theprocess.

When it has been determined in Step S205 that there has been noconvergence in the amount of power received (NO), the control processbranches to Step S206. In Step S206, the laser power transmitting device110 adjusts the direction of laser emission by adjusting the two-axistilt angle of the reflective mirror, and loops the control process toStep S204. When it has been determined in Step S205 that there has beenconvergence in the amount of power received (YES), the control processbranches to Step S207, the process is ended, and the system returns tothe original control process shown in FIG. 4. As a result, alignment ofthe wireless communication link and wireless power supply link betweenthe power transmitting device 110 and the power receiving device 150 isended.

FIG. 11 is a diagram used to explain laser emission alignment in theprior art. A laser beam typically has a spot diameter of several dozenmicrometers or less. A laser beam emitted from a laser powertransmitting device 500 with high directionality is difficult for thelaser power receiving device 510 to observe and align. In the prior artshown in FIG. 11, a reflective panel 512 having a predetermined width isinstalled on the laser power receiving device 510, and the laser beamreflected by the reflective panel 512 is observed and finely adjustedusing an imaging device 502 installed in the laser power transmittingdevice 500.

Therefore, the position of the beam spot 524 observed in an image 520 onthe imaging device 502 has to be detected using image processing whileadjusting the direction of laser emission so that the beam spot iswithin the light-receiving region 522 of the laser power receivingdevice 510. This image process is resource-intensive and requires areflective panel, thus increasing instrumentation costs.

In contrast, rough alignment is performed in the embodiments describedabove via beam forming using the wireless communication link describedabove to roughly fit the beam spot into the light-receiving region.After the rough alignment has been completed, the power transmittingdevice 110 performs fine adjustments by receiving feedback via thewireless communication link on the actual amount of power received bythe power receiving device 150. As a result, a reflective panel 512,imaging device 502 and image processing IC are not required, thusholding down any increase in instrumentation costs.

The following is an explanation with reference to FIG. 10 of power whichcan be supplied using a configuration in which anomalies are detected onthe basis of data communication via the wireless communication linkdescribed above, and the laser output of the wireless power supply linkis controlled in response to the occurrence of an anomaly.

As described above, the reaction time (turnaround time or TAT) from theoccurrence of an anomaly to the reduction in laser output can beshortened to the extent that the response delay time of the wirelesscommunication link is shortened. Thus, laser emission can be achieved ata higher output under conditions meeting exposure standards to theextent that the response delay time is shortened. FIG. 10 is a graph inwhich total power feeding (W) that meets Class 1 safety standardsaccording to JIS C 6802 has been plotted with respect to emissionduration (s). The following explanation will specifically use Class 1,but this is for illustrative purposes only. There are no restrictions onclass.

According to Annex I (Exposure Limits Related to Class 1 Laser Devices)of the Measures For Preventing Damage Due to Laser Beams published bythe Japan Advanced Information Center of Safety and Health(http://anzeninfo.mhlw.go.jp/anzen/hor/hombun/hor1-29/hor1-29-16-1-0.htm),the accessible emission limit (AEL) in Class 1 is 2.4×10⁻⁵ J at anemission duration of t>10⁻⁹ s and at a wavelength from 200 to 302 nm.When the reaction time (TAT) up to the point where laser emission isstopped is T [s], this T [s] becomes the emission duration. Because theupper limit on the emission duration T [s] is 2.4×10⁻⁵ J, the emittedenergy (emitted output) per second during T [s] is 2.4×10⁻⁵/T[W]. It isclear from FIG. 10 that the amount of power supplied increases as thereaction time T decreases under conditions meeting exposure standards.

As shown in FIG. 10, the TAT for wireless LAN communication in frequencybands 2.4 GHz and 5 GHz range from 1.0×10⁻⁴ to 1.0×10⁻³ s according toIEEE 802.11 (The Institute of Electrical and Electronics Engineers,Inc.). In these frequency bands, the directionality is limited and theTAT lengthens as latency is increased due to the Carrier Sense MultipleAccess/Collision Detection (CSMA/CD) method. In the CSMA/CD method,efficiency declines significantly as the number of connected clientsincreases. In an actual environment, therefore, the TAT of wireless LANis in the range of several dozen ms. Therefore, when a wireless LANcommunication link is used, the limit is 1 mW in an actual environmentunder the Class 1 standards.

Millimeter waves have a frequency from 30 to 300 GHz, and millimeterwave wireless communication is typically known to use the 60 GHzfrequency band. However, electromagnetic waves in these frequency bandshave high directionality and can form a direct link, thereby reducingthe response delay time after the establishment of the link. Also,millimeter wave wireless communication in which a direct link is formedhas a shorter TAT than wireless LAN communication using the CSMA/CDmethod described above, and the method does not cause an increase inlatency.

As shown in FIG. 10, the millimeter wave TAT can be in the range of1.0×10⁻⁶ [s]. Therefore, the supply of approximately 10 W of power canbe anticipated even under Class 1 standards. If power could be suppliedin watt units, the power consumption needs of various loads could besatisfied, and the range of devices using a wireless power supply couldbe increased. By using recently developed millimeter wave wirelesscommunication or terahertz wave communication in a frequency band higherthan presently used (at a frequency from 100 GHz to 10 THz), responsetimes TAT can be further reduced, and the supply of power at even higheroutputs can be anticipated.

Because a direct link is formed in millimeter wave wirelesscommunication and the wireless communication link can be continuouslymaintained between wireless stations, it is advantageous to stablymaintain the response delay time described above during laser emission.Also, in millimeter wave wireless communication, the directionality withthe station on the other end of the direct link is optimized using beamforming, and the response delay time is continuously being optimized.Because millimeter waves have greater directionality thanelectromagnetic waves with a long wavelength, the alignment processusing beam forming described above is performed more advantageously.

In the embodiments of the present invention explained above, a powertransmitting device, power receiving device, power supply system andpower supply method can be provided which are able to transmit power viathe emission of electromagnetic waves while also meeting standards forexposure that is likely to occur when an anomaly occurs. The embodimentsof the present invention are also able to increase the powertransmission output via the emission of electromagnetic waves while alsomeeting standards for exposure that is likely to occur when an anomalyoccurs.

The configuration of the embodiments described above allows the powercable between a commercial power source and a power receiving device(the “last wire”) to be eliminated. The power receiving device can beany device able to receive a supply of power via the emission ofelectromagnetic waves and supply the received power to a load. Preferredexamples of power receiving devices include electronic devices for whichthe cost of installing a land line is high, such as projectors andmonitoring cameras installed in high places that can be access pointsfor millimeter wave wireless communication. Because the supply of largeamounts of power can be anticipated from wireless power feeds using themagnetic field resonance method, these power receiving devices may alsobe devices consuming a large amount of power such as personal computers,tablet computers, and mobile phones. Relay devices may also beconfigured to relay wireless data communication and the wireless supplyof power. These devices have the configuration of both power receivingdevices and power transmitting devices.

Some or all of the functional components can be installed in aprogrammable device (PD) such as a field-programmable gate array (FPGA)or integrated into an application-specific integrated circuit (ASIC),and the circuit configuration data (bit stream data) downloaded to thePD such that said functional components may be realized on the PD anddata written in HDL (hardware description language) VHDL (VHSIC (Veryhigh-speed integrated circuit) hardware description language) andVerilog-HDL, etc., for generating the circuit configuration data can bedistributed via a storage medium.

In the embodiments of the present invention, the maximum permissibleexposure (MPE) and the accessible emission limit (AEL) were explained asan example. There are no particular restrictions on the exposurestandards. The exposure standards include any type of exposure. Inaddition to exposure of the human body to electromagnetic waves, theexposure standards may include exposure of animals and objects toelectromagnetic waves. The exposure standards may also be standardsdefining the acceptable amount of exposure or amount of exposurerecommended as an upper limit for any of these types of exposure.

The present invention was explained with reference to embodiments.However, the present invention is not limited to the embodimentsexplained above. The present invention can be altered in any wayconceivable by a person skilled in the art, including other embodiments,additions, modifications, and deletions. Any aspect realizing theactions and effects of the present invention is within the scope of thepresent invention.

KEY TO THE DRAWINGS

100: Laser power supply system

102: Power source

110: Laser power transmitting device

112: Antenna

114: Laser element

120: Wireless data communication unit

122: Maximum output calculating unit

124: Laser output control unit

126: Anomaly detecting unit

128: Laser emitter for power transmission

130: Initial alignment unit

132: Subsequent alignment unit

150: Laser power receiving device

152: Antenna

154: Photoelectric conversion element

160: Wireless data communication unit

162: Photoelectric converter for power reception

164: Anomaly detecting unit

190: Load

What is claimed is:
 1. A power transmitting device able to transmitpower to a power receiving device by emitting electromagnetic waves, thepower transmitting device comprising: a calculating unit for calculatinga maximum value for an emitted output of electromagnetic waves meetingexposure standards on a basis of a response delay time measured by awireless communication link between the power transmitting device andthe power receiving device, wherein each of the power transmittingdevice and the power receiving device is capable of transmitting datathrough the wireless communication link; a power transmitting unit fortransmitting power via a power supply link with the power receivingdevice at an output not exceeding the maximum value; an anomalydetecting unit for detecting anomalies in the power supply link on thebasis of communication with the power receiving device via the wirelesscommunication link, wherein the anomaly detecting unit is furtherconfigured to detect an anomaly in the wireless communication link; andan output control unit for limiting the output on the basis of the adetection of an anomaly in the power supply link, wherein the outputcontrol unit is configured to limit the output in response to anoccurrence of the anomaly in either the wireless communication link orthe power supply link.
 2. The power transmitting device according toclaim 1, wherein the emitted output of electromagnetic waves hasdirectionality, the calculating unit calculates the maximum value forthe emitted output of electromagnetic waves on the a basis of conditionspreventing a predetermined exposure level from being exceeded whenelectromagnetic waves are emitted at a maximum value over a reactionperiod at least including the response delay time, and the outputcontrol unit stops the emitted output of electromagnetic waves in thepower supply link in response to the detection of the anomaly in thepower supply link.
 3. The power transmitting device according to claim2, wherein the anomaly detecting unit detects the occurrence of theanomaly in the power supply link by comparing an amount of powerreceived by the power receiving device via the wireless communicationlink to an amount of power transmitted by the power transmitting device.4. The power transmitting device according to claim 2, wherein theanomaly detecting unit detects the occurrence of the anomaly in thepower supply link by notification received from the power receivingdevice via the wireless communication link of a comparison of an amountof power transmitted by the power transmitting device to an amount ofpower received by the power receiving device.
 5. The power transmittingdevice according to claim 1, wherein the calculating unit repeatedlyevaluates the response delay time in communication via the wirelesscommunication link and calculates the maximum value on the basis of anevaluated response delay time, and the power transmitting unit transmitspower via the power supply link on a basis of a latest calculatedmaximum value.
 6. The power transmitting device according to claim 1,wherein the wireless communication link has directionality, and thepower transmitting device comprises an initial alignment unit foraligning the power supply link via establishment of the wirelesscommunication link, and a subsequent alignment unit for adjusting analignment of the power supply link on the basis of an amount of powerreceived by the power receiving device via the power supply link ascommunicated via the wireless communication link.
 7. The powertransmitting device according to claim 1, wherein the emitted output ofelectromagnetic waves is laser emission, and the wireless communicationlink is a millimeter wave wireless communication link.
 8. A power supplysystem including a power transmitting device able to transmit power byemitting electromagnetic waves, and a power receiving device able toreceive power supplied by the power transmitting device, the powersupply system comprising: a calculating unit for calculating a maximumvalue for an emitted output of electromagnetic waves meeting exposurestandards on the basis of a response delay time measured by a wirelesscommunication link between the power transmitting device and the powerreceiving device, wherein each of the power transmitting device and thepower receiving device is capable of transmitting data through thewireless communication link; a power transmitting unit in the powertransmitting device for transmitting power via a power supply link withthe power receiving device at an output not exceeding the maximum value;an anomaly detecting unit for detecting anomalies in the power supplylink on the basis of communication with the power receiving device viathe wireless communication link, wherein the anomaly detecting unit alsodetects any anomaly in the wireless communication link; and an outputcontrol unit in the power transmitting device for limiting the output ona basis of a detection of an anomaly in the power supply link, whereinthe output control unit limits the output in response to an occurrenceof the anomaly in at least either the wireless communication link or thepower supply link.
 9. A power supply method executed between a powertransmitting device able to transmit power by emitting electromagneticwaves, and a power receiving device able to receive power supplied bythe power transmitting device, the power supply method comprising thesteps of: evaluating a response delay time for communication via awireless communication link between the power transmitting device andthe power receiving device, wherein each of the power transmittingdevice and the power receiving device is capable of transmitting datathrough the wireless communication link; calculating a maximum value foran emitted output of electromagnetic waves meeting exposure standards onthe basis of the response delay time; and causing, by an output controlunit, the power transmitting unit to transmit power via a power supplylink with the power receiving device at an output not exceeding themaximum value, wherein the output control unit limits the output inresponse to an occurrence of an anomaly in at least either the wirelesscommunication link or the power supply link; the power supply methodfurther comprising the steps of: detecting, by an anomaly detectingunit, the anomaly in the power supply link on the basis of communicationwith the power receiving device via the wireless communication link; andcausing the power supply device to limit the output of the power supplylink on the basis of the detection of the anomaly in the power supplylink.
 10. The power supply method according to claim 9, wherein theemission of electromagnetic waves has directionality, the calculatingstep includes calculating the maximum value for the emission output ofelectromagnetic waves on the basis of conditions preventing apredetermined exposure level from being exceeded when electromagneticwaves are emitted at a maximum value over a reaction period at leastincluding the response delay time, and the output limiting step includescausing the power transmitting device to stop the emission output ofelectromagnetic waves in the power supply link in response to thedetection of the anomaly in the power supply link.
 11. The power supplymethod according to claim 10, wherein the anomaly detecting step furthercomprises the steps of causing the power transmitting device to receivean amount of power received by the power receiving device via thewireless communication link, and causing the power transmitting deviceto detect the occurrence of anomalies in the power supply link bycomparing the amount of power received to an amount of power transmittedby the power transmitting device.
 12. The power supply method accordingto claim 10, wherein the anomaly detecting step further comprises thesteps of causing the power transmitting device to transmit the amount ofpower transmitted by the power transmitting device to the powerreceiving device via a communication device, causing the power receivingdevice to detect any anomaly occurring in the power supply link on thebasis of a comparison of the amount of power transmitted to the amountof power received by the power receiving device, and causing the powerreceiving device to notify the power transmitting device of any detectedanomaly.
 13. The power supply method according to claim 9, wherein thewireless communication link has directionality, and the power supplymethod, prior to the power transmitting step, further comprises thesteps of: initially aligning the power supply link via establishment ofthe wireless communication link, and adjusting an alignment of the powersupply link on the basis of an amount of power received by the powerreceiving device via the power supply link as communicated via thewireless communication link.
 14. The power supply system of claim 8,wherein the emission, by the power transmitting device, ofelectromagnetic waves is laser emission, and wherein the power receivingdevice includes a photoelectric conversion element and receives a laserbeam emitted by the laser power transmitting device via thephotoelectric conversion element, further comprising: a first antennaattached to the power receiving device; and a second antenna attached tothe power transmitting device, wherein the first antenna and the secondantenna are configured to establish wireless data communication via thewireless communication link.
 15. The power supply method of claim 9,wherein the emission, by the power transmitting device, ofelectromagnetic waves is laser emission, and wherein the power receivingdevice includes a photoelectric conversion element and receives a laserbeam emitted by the laser power transmitting device via thephotoelectric conversion element, further comprising: receiving, by aload attached externally to the power receiving device, the emittedlaser beam, wherein the load is a secondary battery.
 16. The powersupply method of claim 9, wherein the emission, by the powertransmitting device, of electromagnetic waves is laser emission, andwherein the power receiving device includes a photoelectric conversionelement and receives a laser beam emitted by the laser powertransmitting device via the photoelectric conversion element, furthercomprising: receiving, by a load attached internally to the powerreceiving device, the emitted laser beam, wherein the load is amonitoring camera.